This research will examine factors regulating the expression of voltage- and Ca2+-activated ionic channels during the embryonic development of parasympathetic ciliary ganglion (CO) neurons of the chick. Jonic channels are critical for the normal function as well as the formation of vertebrate neural networks, but very little is known about the factors that control their functional expression during development, including the possible role of interactions with other cells, neurotrophic factors, and/or posttranslational modification. However, these epigenetic factors regulate nearly every other aspect of the normal development and differentiation of vertebrate neurons. CO neurons offer many important technical advantages for developmental and electrophysiological investigations. Preliminary work indicates that epigenetic factors are required for the normal developmental expression of many of these channels. These experiments will utilize procedures performed in situ and in vitro to examine the role of target tissues, the afferent innervation, selected neurotrophic factors, and neuronal and neuromuscular activity in the regulation of the expression of three classes of ionic channels important for the normal function of these cells. These channels give rise to A-currents (IA), Ca2+- activated K+ currents (IK[Ca]) and voltage-activated Ca2+ currents (ICa). The expression of ionic channels will be determined by using several configurations of the patch-clamp recording technique on acutely-isolated and cultured CG neurons. For each of these currents, experiments will be performed in which CG neurons develop in situ and in vitro in the presence and absence of their normal target tissues, and in the presence and absence of innervation. The role of phosphorylation in the developmental regulation of these channels will also be examined by means of selective protein kinase and phosphatase inhibitors, kinase activators, and exogenous kinases and nucleotides applied to the cytoplasmic face of the plasma membrane as well as in whole-cell recordings. The actions of relevant neurotrophic factors on channel expresion will be studied, and we will determine if the effects of these factors are dependent on transcription or translation. The appropriate expression of ensembles of ionic channels is necessary for the normal function of neural networks. Abnormalities in the developmental expression of ionic channels could underlie a variety of disease states, and may contribute to the pathophysiology of various neurodegenerative disorders. in additon, this research will provide increased understanding of the actions of neurotrophic factors, potential therapeutic agents for the treatment of traumatic and degenerative disorders of the nervous system.